(a) Field of the Invention
The present invention relates to a system for a hybrid vehicle. More particularly, the present invention relates to a system for a hybrid vehicle that is applied to a plug-in hybrid vehicle and enhances driving performance at an electric vehicle (EV) mode.
(b) Description of the Related Art
A hybrid vehicle is a vehicle that uses two or more distinct power sources to move the vehicle. The term most commonly refers to hybrid electric vehicles (HEVs), which combine an internal combustion engine and one or more electric motors powered by a battery. However, alternative forms of hybrid vehicles do exist, Hybrid Fuel cell vehicles.
Hybrid vehicles have become increasingly popular over the last couple of years due to their high fuel efficiency and low impact on the environment.
A conventional hybrid system, as shown in FIG. 1A, typically includes two motors 3 and 5 and a power delivery device 4 (e.g., a clutch). Engine starting and generation of electricity is performed typically by a first motor 3 (e.g., Hybrid Starter Generator: HSG) disposed on an engine side and driving and regenerative braking is performed by a second motor 5 disposed on a transmission side. In addition, a clutch 4 operates as a power delivery device for engaging and disengaging torque from the engine to the transmission 2.
When the vehicle operates in an electric vehicle mode, the engine 1 is disconnected from the transmission 2 via the clutch 4 and the vehicle is driven only by power from the motor 5 as shown in FIG. 1B. When the vehicle operates in a hybrid mode, the clutch 4 between the engine 1 and the motor 1 is operated and driving torque of the engine is transmitted to the transmission 2 as shown in FIG. 1C.
Recently, however, manufactures have begun to introduce another type of hybrid vehicle known as a plug-in hybrid vehicle (PHEV). In a PHEV, capacity of the battery is increased compared with a conventional hybrid batteries and the battery is charged via commercial electricity rather than by regenerative braking or a generator. Therefore, these vehicles allow a driver to operate the vehicle using just electrical energy (i.e., an EV mode) when driving short distances and operate the vehicle in a conventional HEV mode once the battery has been discharged.
Thus a PHEV can be driven by using both or either of the internal combustion engine and the electric motor depending upon how far the driver is driving. In these types of hybrid vehicles, a high-voltage battery which can be easily charged by electricity and typically having a large capacity is mounted in somewhere within the plug-in hybrid vehicle.
Because the hybrid vehicle are typically expect to perform much like conventional internal combustion vehicles, enhanced driving performance while in the electric vehicle mode is expected by consumers as well and thus, output capacity of the electric motor should be increased compared to a conventional hybrid vehicle.
In order to increase the output capacity of the electric motor, increase of material cost is often as a result unavoidable and total manufacturing cost resultantly increases, as well.
Further, since the second motor/generator MG2 is in charge of providing the entire power output for driving the vehicle and the first motor/generator MG1 is used for engine starting and generating electricity during the EV mode only. Thus, sufficient driving performance cannot be guaranteed through the second motor/generator MG2 operating in the EV mode.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.